1. Field of the Invention
The present invention relates to an apparatus and a method for baking a photoresist, and more particularly, to an apparatus and a method for soft baking a photoresist before performing an exposing process.
2. Description of the Related Art
Recently, portable electronic devices such as a mobile phone, a PDA, and a notebook computer have been widely used. Therefore, there is a strong demand for a flat panel display device with light weight and compact size. The flat panel display device such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), a vacuum fluorescent display (VFD), etc. have been actively researched and developed. Among the above display devices, the LCD device that can be easily driven, massively produced, and realized with high picture quality is in the spotlight.
The LCD device includes an array substrate having pixels, a color filter substrate facing the array substrate for displaying colors, and a liquid crystal layer formed between the array substrate and the color filter substrate. An electric field applied on the liquid crystal layer controls an alignment direction of the liquid crystal layer.
A switching device such as a thin film transistor for driving the pixel is arranged adjacent to the pixel on the array substrate. The thin film transistor is fabricated by using a semiconductor fabricating process, including a photolithography process using a photoresist pattern.
The photolithography process includes a process for depositing a thin film on a substrate, a process for applying a photoresist on the thin film, a process for exposing the photoresist, a process for developing the photoresist, a process for etching the thin film by using the developed photoresist pattern, a process for stripping the photoresist pattern, and a process for washing the substrate.
The process for patterning a photoresist is referred to as a photo process. The photo process includes a process for surface-processing a substrate so that a photoresist can be smoothly deposited on the substrate, a process for depositing a photoresist on the substrate, a soft baking process for removing a solvent in the deposited photoresist, a process for applying a mask to the soft baked photoresist and exposing the soft baked photoresist, a process for developing the exposed photoresist, and a hard baking process for hardening the photoresist developed so that the photoresist is formed as a certain pattern. The photoresist can be uniformly deposited on the substrate by a spin coating method.
Referring to FIGS. 1A and 1B, a soft baking apparatus is inside a chamber in which the soft baking process and the hard baking process are mainly performed. The soft baking apparatus will be explained in more detail hereinbelow.
The soft baking process is performed in order to remove a part of a solvent in the deposited photoresist. Therefore, the soft baking apparatus is provided with a heating plate for heating the substrate on which a photoresist is deposited and for evaporating the solvent in the photoresist.
The soft baking apparatus is divided into a contact type soft baking apparatus and a non-contact type soft baking apparatus. For the contact type soft baking apparatus, the substrate 102 is in direct contact with a heating plate 101 as shown in FIG. 1A. For the non-contact type soft baking apparatus, the substrate 102 is spaced apart from the heating plate 101 by a certain distance as shown in FIG. 1B. A heating wire 103 for supplying heat to the heating plate 101 is installed in the heating plate 101.
For the contact type soft baking apparatus, since the substrate is in direct contact with the heating plate 101 in which a heating wire is installed, the heat distribution may be non-uniform on the substrate. Therefore, as shown in FIG. B, the non-contact soft baking apparatus is developed. As shown in FIG. 1B, the substrate 102 is spaced apart from the heating plate 101 by a certain distance by a plurality of lift pins 104.
FIGS. 2A and 2B are top views showing a substrate 200 spaced apart from the heating plate 101 by a plurality of lift pins 202 formed on the heating plate 101. As shown in FIGS. 2A and 2B, the substrate 200 is divided into an LCD panel region 201 and a non-LCD panel region 204, i.e., the dummy region.
The lift pins 202 formed on the heating plate are constructed to be simultaneously lifted or lowered. Before the substrate is introduced into the soft baking apparatus, the lift pins 202 are lifted and wait for the substrate to be loaded. All the lift pins 202 are simultaneously lifted by a certain height from the upper surface of the heating plate. Then, the substrate 200 is loaded on the lift pins 202 for a soft baking process.
However, a contact region of the substrate contacted by the lift pins 202 and a non-contact region of the substrate are heated at different temperatures during the soft baking process. Therefore, the photoresist on the contact region and the non-contact region has different drying speeds and contraction degrees, which cause an inferior baked photoresist pattern in the exposing process.
That is, since the contact region and the non-contact region have different heating speeds and cooling speeds, spots are generated on the substrate in the exposing process. Therefore, it is important to make sure that the lift pins do not contact the LCD panel region in order to have a uniform baked photoresist in the LCD panel region before performing the exposing process.
However, since the LCD panel region may be arranged on different substrates in different ways, the LCD panel region of a certain substrate may not be in contact with the lift pins, but the LCD panel region of another substrate may be in contact with the lift pins, thereby causing spots on the substrate in the exposing process.
FIGS. 2A and 2B show two different arrangements of the LCD panel region on two different substrates that are loaded into a soft baking apparatus with all-lifted lift pins. FIG. 2A shows that the lift pins 202 are not in contact with the smaller-size LCD panel region 201. FIG. 2B shows that the lift pins 202 are in contact with the larger-size LCD panel region. In the case of FIG. 2B, spots may be generated on the LCD panel region when the soft baked photoresist is exposed to light.